This invention relates to the field of electrical devices for sensing or measuring magnetic fields. In particular, the present invention is directed to an apparatus for containing electrical components for sensing or measuring magnetic fields.
Hall effect transducers are used to measure speed and/or sense the direction of rotation in various machines including pumps, motors, and engines including automobile engines. Hall effect sensors such as those described in the publication "Hall Effect Transducers" by MicroSwitch of Freeport, Ill. in 1982 are well known in the art. Hall effect transducers may be used to measure the speed or sense the direction of rotation of shafts having magnetic rings thereon such as those described in U.S. Pat. No. 5,224,259. Biased Hall effect transducers contain a magnet and may be used to measure the rotation of gears or sprockets made of a ferritic material. These types of devices are typically contained in an apparatus and mounted within the housing of a pump, transmission, motor or the like.
Containers for such electrical devices are generally holes in tough and strong non ferrous materials such as stainless steel. Strength and toughness is particularly required so that the end membrane thickness may be minimized to pass the magnetic flux most easily, and yet have structural integrity in the presence of significant fluid pressures. Typically, these sensor containers are made of a one-piece construction in the form of a closed end tube having a flat end thereof through which magnetic fields travel to be sensed by the Hall effect sensors. However, this one piece construction creates particular manufacturing problems because of the difficulty in manufacturing closed end tubular devices of a non-ferrous metal. In particular, it is difficult to create long and narrow holes in non-ferrous materials such as stainless steel. Since materials such as stainless steel have a low thermal conductivity, it is difficult to achieve sufficient cooling of a cutting tool such as a flat bottom drill or end mill used to create elongate hollow tubular members out of non-ferrous metals. Moreover, the use of non-ferrous metals such as stainless steel is relatively more expensive than ferrous metals such as carbon steel.
It is therefore desirable to create an apparatus for containing electrical components for sensing or measuring magnetic fields therethrough which are easily manufacturable and which is not difficult to drill elongate holes therethrough. It is also desirable to create such an apparatus by minimizing the amount of non-ferrous metals such as stainless steel required to be used therein. In this regard, it is also desirable to utilize ferrous metals for the container while still allowing the sensors therein to be capable of sensing magnetic fields.
The containers for these sensors typically have end portions which are made of a thin non-ferrous material so that transducers may be held in close proximity to a rotating magnet or rotating gear or sprocket.